The present invention relates to an external storage device system. More specifically, the present invention relates to a technology for prolonging an operation period of a disk device (hereafter also referred to simply as a disk) and decreasing power consumption of a storage device system (hereafter referred to as a disk array). Here, the disk device's operation period signifies a period from the time to start using the disk device to the time when the disk device becomes unusable.
A disk array is a type of storage device systems connected to a computer. The disk array is also referred to as a RAID (Redundant Arrays of Inexpensive Disks) and constitutes a storage device system comprising a plurality of disk devices arranged in an array and a control section to control them. The disk array concurrently operates disk devices to accelerate read requests (requests to read data) and write requests (requests to write data) and to provide data with redundancy. Disk arrays are categorized into five levels depending on types of redundant data to be added and disk array configurations. This is described in non-patent document 1 (Daved A. Patterson, Garth Gibson, and Randy H. Katz, “A Case for Redundant Arrays of Inexpensive Disks (RAID)”, Computer Science Division Department of Electrical Engineering and Computer Sciences, University of California Berkeley, 1988).